Hi
I have a data set consisting of pictures on which individual plants were
identified and categorized into "alive", "dead" and "unknown" if it was
not clear. The time of these pictures ranges from 1937 to today and the
intervals range between 13 and 1 year.
I am trying to get an understanding of the mortality rate which I can
then use in an individual based model.
Therefore I thought of using survival analysis. I have ordered my data
in the required format, and classified the events as "interval censored"
(event=3) for the cases where the plant died and "right censored"
(event=0) but I have still a problem
I managed to obtain a Surv() object by calling
> surv <- with(survival, Surv(time, time2, event, type="interval"))
where survival is my dataset
> surv
[1] [13, 16] 68+ 16+ 68+ 68+ 68+ [26, 34] 68+
[9] 68+ 16+ [54, 58] [64, 67] 68+ [34, 54] [34, 54]
[58, 63]
[17] [48, 58] [48, 63] [34, 54]
And it looks correct (I set the year 1937 to 0)
But where to from here? I understand that most of the analysis can not
be done with interval censored data? As far as I understand it, I have
to use interval censored as the observation intervals are not equal and
in addition quite large.
The data is from one site, no interference.
As I said, I would like to have an estimate of the hazard function (I
guess) to get information about the mortality rate of the individuals.
Any help welcome,
Rainer
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Rainer M. Krug, Dipl. Phys. (Germany), MSc Conservation
Biology (UCT)
Leslie Hill Institute for Plant Conservation
University of Cape Town
Rondebosch 7701
South Africa
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